Yes you can use DUAL QPI XEONS on an X58 board. Look at my sig rig. DUAL QPI means it will only run in a MAX 2 CPU configuration. The new 2011 E5 chips will more than likely be QUAD QPI. Meaning the MAX configuration they can run is 4 processors together on one board.

If you go the SR-3 option you should be able to start off with just one processor and then upgrade to two later but both of your processors WILL have to match.

Ooooh max 4 cpu's you say? Well they should really launch an sr-3+ or sr-4 board then for those who want a little more crazy.